The present invention relates to a skate with single-rail truck, particularly with in-line wheels.
Conventional skates with in-line wheels that are already commercially available have a plurality of wheels, generally three to five according to the kind of use, which are aligned and are supported by a frame, generally made of metal, that is connected to the lower part of a shoe which can be variously shaped.
The wheel supporting frame is typically shaped like an inverted U, with parallel side walls which are perpendicular to the ground and have holes, inside which the shafts for the pivoting of the respective wheels are fixed.
The typical drawback of these skates resides in the fact that the movements of the athlete, especially with reference to certain sports in which it is very often necessary to be able to tilt the skate beyond conventional angles, so that it is almost parallel to the ground, as occurs for example in hockey, are hindered because interference with the ground would occur.
Accurate tests have allowed to determine that the limitation of the angle of incidence with respect to the ground is caused not so much by the shoe but rather by the shape of the wheel and by the presence of the frame shaped like an inverted U, because this cross-section necessarily entails a considerable bulk which contributes to loss of wheel grip once a certain limit is exceeded.
In order to eliminate this drawback, in-line skates have already been marketed wherein the supporting frame is substantially rail-shaped, providing support for the axle of the wheels, which are advantageously provided by means of two wheel halves arranged on opposite sides with respect to the rail-shaped frame.
Embodiments of this type are disclosed for example in U.S. Pat. No. 2,166,766 and EP 0 127 734 patents.
In this embodiment, the pivot or axle for the rotation of the wheel is rigidly coupled to the rail-shaped structure of the frame and the wheels are connected to the pivot by means of two bearings, wherein the inner part is fixed with respect to the pivot and the outer part is fixed with respect to the wheels.
With this embodiment, the two wheel halves are independent from one another, so that during changes in direction, when the lateral inclination of the skate varies and therefore contact with the ground shifts from one wheel half to the other, poor reactivity of the skate inevitably occurs. The wheel half that makes contact with the ground, by being substantially motionless, in fact produces energy losses. This aspect is important especially in hockey, where quick and frequent changes in direction, with very tight curving radii and with the smallest possible energy loss, are required.
It should in fact be noted that when changing direction, the wheel half that begins to make contact with the ground would have a rotation rate of approximately zero and, in an infinitesimal time, would have to reach the value of the instantaneous rotation rate of the other wheel half; it is evident that the mass of the wheel does not start to move instantaneously, due to inertia, and therefore a significant energy loss occurs.
Other known solutions, such as for example those disclosed in U.S. Pat. No. 5,069,462 and U.S. Pat. No. 2,570,349 patents, provide for a wheel constituted by two mutually rigidly coupled half-shells, and therefore the rotation rate would not be different even during direction changes; however, in these solutions the wheel is supported by a single bearing contained within the thickness of the single-rail truck.
Supporting the wheel halves by means of a single central bearing inevitably entails considerable instability on the wheel halves, with consequent vibrations which make it difficult to control the skate; this occurs due to the intense stresses discharged onto the bearing, particularly those acting along directions other than the vertical with respect to the ground; the stress to which the bearing is subjected therefore rapidly produces wear and plays among the various components, leading to the above-mentioned instability due to loss of coupling precision.